ALSA: pci: Constify snd_rawmidi_ops

Now snd_rawmidi_ops is maintained as a const pointer in snd_rawmidi,
we can constify the definitions.

Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/echoaudio/midi.c

@@ -288,13 +288,13 @@ static int snd_echo_midi_output_close(struct snd_rawmidi_substream *substream)
 
 
 
-static struct snd_rawmidi_ops snd_echo_midi_input = {
+static const struct snd_rawmidi_ops snd_echo_midi_input = {
 	.open = snd_echo_midi_input_open,
 	.close = snd_echo_midi_input_close,
 	.trigger = snd_echo_midi_input_trigger,
 };
 
-static struct snd_rawmidi_ops snd_echo_midi_output = {
+static const struct snd_rawmidi_ops snd_echo_midi_output = {
 	.open = snd_echo_midi_output_open,
 	.close = snd_echo_midi_output_close,
 	.trigger = snd_echo_midi_output_trigger,